The implementation of advanced process control methods in integrated circuit fabrication, such as semiconductor device manufacturing of the type that uses monolithic substrates of group IV materials such as silicon or germanium or group III–V compounds such as gallium arsenide, has been primarily focused on the early detection and automatic root cause analysis of process problems. A significant portion of this effort deals with identifying so-called killer defects and controlling the level of such on production substrates. Frequently, defects that are traceable to a particular process problem appear in visually recognizable or spatially repeating patterns. The detection of such repeating defect clusters, signatures, and individual defects is an important and useful indicator of a process problem. It is particularly effective for the early detection of process excursion conditions when defect patterns on the substrate are not yet fully developed.
Spatial correlation of substrate defects is a common practice in current process control systems. For example, defect source analysis correlates spatial defects between process steps of individual substrates and source steps for each defect. Repeater analysis looks for defects on a substrate that repeat with the periodicity of reticle steppers. Repeater analysis is therefore performed to identify reticle defects. However, all of these analyses are based on a defect to defect correlation rather than on a more global cluster to cluster correlation.
Defect to defect correlations are useful in identifying physically identical sources of the defects, such as defects that propagate through processing steps or reticle irregularity. However, defect correlations are less useful for identifying process problems across substrates that underwent common process steps. The defect level correlation is often quite weak in such cases.
What is needed, therefore, is a system for identifying process problems that do not necessarily have a strong correlation with the spatial location or spatial repetition of individual defects.